LONDON (Reuters) - Air pollution killed about 7 million
people in 2012, making it the world's single biggest
environmental health risk, the World Health Organization (WHO)
said on Tuesday.

The toll, a doubling of previous estimates, means one in
eight of all global deaths in 2012 was linked to polluted air
and shows how reducing pollution inside and outside of people's
homes could save millions of lives in future, the United Nations
health agency said.

Air pollution deaths are most commonly from heart disease,
strokes or chronic obstructive pulmonary disease. It is also
linked to deaths from lung cancer and acute respiratory
infections.

"The evidence signals the need for concerted action to clean
up the air we all breathe," said Maria Neira, head of the WHO's
environmental and social public health department.

"The risks from air pollution are now far greater than
previously thought or understood, particularly for heart disease
and strokes," she said.

Poor and middle-income countries in southeast Asia and the
Western Pacific region had the largest air pollution-related
burden in 2012, with 3.3 million deaths linked to indoor air
pollution and 2.6 million deaths to outdoor air pollution.

Indoor pollution is mostly caused by cooking over coal, wood
and biomass stoves. The WHO estimates that around 2.9 billion
people worldwide live in homes using wood, coal or dung as their
primary cooking fuel.

Flavia Bustreo, a WHO family health expert, said women and
children - especially those living in poor countries - often
bear the brunt of the risks from indoor pollution "since they
spend more time at home breathing in smoke and soot from leaky
coal and wood cooking stoves."

Outdoors, air is mainly polluted by transport, power
generation, industrial and agricultural emissions and
residential heating and cooking.

Research suggests outdoor air pollution exposure levels have
risen significantly in some parts of the world, particularly in
countries with large populations going through rapid
industrialization, such as China and India.

The WHO's cancer research agency IARC published a report
last year warning that the air we breathe is laced with
cancer-causing substances and should be officially classified as
carcinogenic to humans.

Carlos Dora, a WHO public health expert, called on
governments and health agencies to act on the evidence and
devise policies to reduce air pollution, which in turn would
improve health and reduce humans' impact on climate change.

"Excessive air pollution is often a by-product of
unsustainable policies in sectors such as transport, energy,
waste management and industry," he said.

"In most cases, healthier strategies will also be more
economical in the long term due to healthcare cost savings as
well as climate gains."